The paper industry produces many different kinds of paper, depending upon its ultimate use. In many cases, the uncoated paper does not have sufficient properties to allow printing directly to the surface. For this reason, paper is often coated with one or more layers in order to render the surface receptive to inks. The coatings are generally made from starch, a thermoplastic polymer, a non-thermoplastic polymer or a combination thereof. Starch, however, tends to form a gelatinous slurry which can be difficult to work with and thermoplastics can be expensive and are not easily recyclable when applied to paper.
There are many requirements for an ink receiving layer, not only for paper, but for any printable surface, for example, plastic sheets and textiles. The ink receiving layer should have a high ink absorbing capacity, so that the dots will not flow out and will not be expanded more than is necessary to obtain a high optical density, even if ink droplet in a multi-color system may be superposed on the same physical spot. The ink receiving layer should have a high ink absorbing speed (short ink drying time) so that the ink droplets will not feather if smeared immediately after applying. The ink receiving layer should be excellent in color forming characteristics. The ink receiving layer must be readily wetted so that there is no “puddling”, i.e. coalescence of adjacent ink dots, and an earlier absorbed ink drop should not show any “bleeding”, i.e. overlap with neighboring or later placed dots. It must have a low haze-value and be excellent in transmittance properties.
After being printed, the image must have a good resistance to water, light, and/or time-dependent discoloration. The ink recording element may not show any curl or sticky behavior if stacked before or after being printed.
To meet these requirements, the ink receptive layers of the prior art have been prepared using many different materials. A dimensionally stable substrate such as polyethylene terephthalate (PET), cellulose triacetate, or paper is used most frequently and coated with one or more polymer coatings. There is a need for an ink receiving layer that can be coated onto multiple substrates and provide all of the properties that are needed for such a layer.